When spinach is fully wilted, add crab and shrimp and cook until shrimp is just beginning to turn opaque, about one minute, then remove from heat. Stir in cream cheese, Gouda, and Gruyere, and add paprika, salt, pepper, and red pepper flakes to taste if desired.

Place entire skillet in the oven, and bake until bubbly and golden, about 15 minutes.

Remove skillet from oven, and let rest for at least 1 minute. Garnish with parsley and red pepper flakes if desired, and serve hot.